Kemper J, Priest A N, Schulze D, Kahl-Nieke B, Adam G, Klocke A
Clinic of Diagnostic and Interventional Radiology, University Medical Center of Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany.
Eur Radiol. 2007 Feb;17(2):533-40. doi: 10.1007/s00330-006-0335-x. Epub 2006 Jun 29.
The objective of this paper is to evaluate magnetic field interactions at 1.5 and 3 T for 20 orthodontic devices used for fixed orthodontic therapy. Twenty springs and auxiliary parts made from varying ferromagnetic alloys were tested for magnetic field interactions in the static magnetic field at 1.5 and 3 T. Magnetic translational force F(z) (in millinewtons) was evaluated by determining the deflection angle beta [American Society for Testing and Materials (ASTM standard test method)]. Magnetic-field-induced rotational force F(rot) was qualitatively determined using a five-point scale. beta was found to be >45 degrees in 13(15) devices at 1.5(3) T and translational force F(z) exceeded gravitational force F(g) on the particular object [F(z) 10.17-261.4 mN (10.72-566.4 mN) at 1.5(3) T]. F(z) was found to be up to 24.1(47.5)-fold higher than F(g) at 1.5(3) T. Corresponding to this, F(rot) on the objects was shown to be high at both field strengths (> or = +3). Three objects (at 1.5 T) and one object (at 3 T) showed deflection angles <45 degrees , but F(rot) was found to be > or = +3 at both field strengths. For the remaining objects, beta was below 45 degrees and torque measurements ranged from 0 to +2. Of 20 objects investigated for magnetic field interactions at 1.5(3) T, 13(15) were unsafe in magnetic resonance (MR), based on the ASTM criteria of F(z). The implications of these results for orthodontic patients undergoing MRI are discussed.
本文的目的是评估用于固定正畸治疗的20种正畸器械在1.5 T和3 T磁场中的磁场相互作用。对20个由不同铁磁合金制成的弹簧和辅助部件在1.5 T和3 T静磁场中进行磁场相互作用测试。通过确定偏转角β[美国材料与试验协会（ASTM标准测试方法）]来评估磁平移力F(z)（以毫牛顿为单位）。使用五点量表定性确定磁场诱导的旋转力F(rot)。发现在1.5（3）T时，13（15）个器械中的β大于45度，并且特定物体上的平移力F(z)超过重力F(g) [在1.5（3）T时F(z)为10.17 - 261.4 mN（10.72 - 566.4 mN）]。发现在1.5（3）T时F(z)比F(g)高24.1（47.5）倍。与此相应，在两个场强下物体上的F(rot)都很高（≥ +3）。三个物体（在1.5 T时）和一个物体（在3 T时）的偏转角<45度，但发现在两个场强下F(rot)都≥ +3。对于其余物体，β低于45度，扭矩测量范围为0至 +2。根据F(z)的ASTM标准，在1.5（3）T下研究磁场相互作用的20个物体中，13（15）个在磁共振（MR）中不安全。讨论了这些结果对接受MRI检查的正畸患者的影响。
